The alignment of a vehicle's wheel plane relative to the path traveled by the vehicle affects not only the handling of the vehicle but also affects the wear on the tires. As used herein, alignment refers to camber, toe, and thrust. Camber is the angle between the vertical axis of the wheel and the vertical axis of the vehicle. Positive camber refers to an angle where the top of the wheel is farther away from the center of vehicle than the bottom of the wheel. Negative camber refers to an angle where the bottom of the wheel is farther away from center of the vehicle than the top. Generally speaking, camber changes of even a fourth of one degree can impact tire wear. Abnormal tire wear has been observed in certain applications with even smaller camber angles changes. Toe is the angle each wheel makes with the longitudinal axis of the vehicle. Positive toe, also referred to as toe in, is a condition where the front of the wheel is pointing in or towards the center line of the vehicle. Negative toe, also referred to as toe out, is a condition where the front of the wheel points out or away from the center line of the vehicle. Generally speaking, toe changes of even one-tenth of a degree can have an impact on tire wear. Thrust is the resulting direction of travel of an axle as opposed to the direction that might be expected from the orientation of the tires on the axle.
When a typical axle is installed under a vehicle (used herein to refer to both motorized vehicles as well as trailers) and placed into normal operation under typical loading conditions, the camber does not remain at zero. The axle under load, although quite rigid, does flex. The flexing of the axle occurs because the suspension is attached to the axle at load transfer points which are significantly inboard of the ends of the axle, but the tires support the weight of the vehicle by means of attachment points which are relatively near the outboard ends of the axle. As a result of this geometry, the weight of the vehicle imposes a bending moment on the axle which in turn causes upward deflection of the ends of the axle resulting in the tires presenting a slight negative camber. As the load increases, the more negative the camber becomes. Once the weight is removed, the axle may recover and again affect the alignment of the wheels. Because of factors such as the additional costs and amount of material that would be required, increasing the stiffness of the axle to resolve camber issues may not be practical.
Even with the same amount of camber on each axle spindle, axle camber affects the tires differently depending on their individual wheel end position on the vehicle because most road surfaces are not flat transversely across the road. When a typical tandem axle vehicle (tractor or trailer) turns while traveling in a forward direction, the dynamics of the vehicle favor lateral grip by the forward axle tires. As a result the pivot point of the vehicle shifts toward the forward axle tires and the rear axle tires will tend to have greater slip laterally as the vehicle negotiates a turn maneuver. For this reason, the rear tires on a tandem axle pair receive more scrub and have a faster wear rate than the tires on the forward axle. Scrub tends to arrest the development of irregular wear and thus the rear tires usually are less affected by the camber issue than are the tires on the forward axle. So as a consequence, the tire irregular wear issue is usually worst on the inboard surface of the left front tire. Next worst is the left rear tire. The right front tire comes next but is sometimes similar in severity to the left rear. The most even wear usually is found on the rear right tire depending upon the particular application, load, and routes normally traveled. It should be obvious that in countries such as Australia, where drivers drive on the left side of the road instead of the right side, the above would be reversed.
One mechanism of adjusting axial alignment involves a system that includes a spindle sleeve that has an outer surface about a first axis of revolution and an inner surface about a second axis of revolution at an angle to the first axis. The predetermined angle may be in a vertical direction to induce a change in camber, in a horizontal direction to induce a change in toe, or a combination thereof. Assembly of such systems onto an axle of a vehicle requires the installer correctly assemble the device and provide the proper amount and type of lubricant to the inside of the hub that contains the spindle sleeve and bearings. In addition, an installer may inadvertently introduce contamination into the assembly to further frustrate proper lubrication of the bearings and other components. It would be desirable to provide a mechanism of affording lubrication to the spindle sleeve and bearings while at the same time avoiding contamination and the possibility of installer error.
The use of identical or similar reference numerals in different figures denotes identical or similar features.